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Test Your Knowledge of the Muscles of Mastication
1. Which of the following is not a primary muscle of mastication?
Mastication is facilitated by four primary muscles and several accessory muscles. The primary masticatory muscles include the temporalis, medial pterygoid, lateral pterygoid, and masseter, whereas accessory contributors include the suprahyoid muscles and the infrahyoid (strap) muscles.1 When the infrahyoid muscles stabilize the hyoid bone, the suprahyoid muscles assist in depressing the mandible against opposing forces.2 Additionally, while the buccinator is primarily a muscle of facial expression, it acts as an accessory muscle of mastication by keeping food positioned for proper mastication.1
References
1. Basit, H., Tariq, M.A., Siccardi, M.A. Anatomy, Head and Neck, Mastication Muscles. (2023, June 5). StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK541027/
2. Khan, Y.S., Fakoya, A.O., Bordoni, B. (2025, March 25). Anatomy, Head and Neck: Suprahyoid Muscle. StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK546710/
2. The muscles of mastication receive their primary arterial supply from the maxillary artery, a branch of the internal carotid artery.
The maxillary artery, a terminal branch of the external carotid artery, provides the primary arterial supply to the muscles of mastication.1,2 Deep temporal arteries, along with contributions from the superficial temporal branch, supply the temporalis muscle. The masseter muscle is supplied directly by the masseteric artery, while the medial and lateral pterygoid muscles are supplied by small pterygoid branches.2
References
1. Basit, H., Tariq, M.A., Siccardi, M.A. Anatomy, Head and Neck, Mastication Muscles. (2023, June 5). StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK541027/
2. Brizuela, M., Al Khalili, Y. Anatomy, Head and Neck, Maxillary Artery. (2025, December 1). StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK542301/
3. All four primary muscles of mastication are innervated by branches originating from the _____ division of the trigeminal nerve.
The mandibular nerve (CN V3) is the third and largest division of the trigeminal nerve (CN V) and the only division carrying both sensory and motor fibers. It further subdivides and provides motor innervation to all four primary muscles of mastication:
- Temporalis: Deep temporal branches
- Masseter: Masseteric nerve
- Medial pterygoid: Medial pterygoid nerve
- Lateral pterygoid: Lateral pterygoid nerve1
Reference
1. Basit, H., Tariq, M.A., Siccardi, M.A. Anatomy, Head and Neck, Mastication Muscles. (2023, June 5). StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK541027/
4. Recent research has confirmed that the masseter muscle consists of how many distinct layers?
Anatomical accounts traditionally characterize the masseter as having two layers (superficial and deep) despite historical anatomists like von Haller in 1784 and various twentieth-century texts describing a potential third layer or distinct fiber orientations.1,2 However, a 2022 study clarified the structure of the masseter and established an anatomically distinct third layer.1 Further research has confirmed the three-layer structure and proposed a reclassified nomenclature of superficial, middle (formerly deep), and deep parts.2
References
1. Mezey, S.E., Müller-Gerbl, M., Toranelli, M., Türp, J.C. The Human Masseter Muscle Revisited: First Description of Its Coronoid Part. Ann Anat. 2022; 240: 151879. https://www.sciencedirect.com/science/article/pii/S0940960221002053
2. Hur, S., Kim, J., Cho, H.J., et al. Reclassification of the Human Masseter Muscle: Anatomical, Histological, and Ultrasonographic Characterization of its Deep Layer. Folia Morphol (Warsz). 2026; 85: e01726004. https://journals.viamedica.pl/folia_morphologica/article/view/109820
5. Trismus is exclusively caused by iatrogenic trauma to the muscles of mastication.
While iatrogenic trauma to the muscles of mastication can cause trismus, it is not exclusively caused by dental treatment complications. Trismus can also result from other underlying etiologies, such as severe dental infections involving the masticatory muscles (e.g., pericoronitis), systemic infections (e.g., tetanus), or space-occupying neoplasms. Additionally, surgery and radiotherapy for head and neck cancer may lead to masticatory muscle fibrosis and the development of trismus, with risk increasing if the medial pterygoid muscle lies within the radiation field.1
When iatrogenic trauma to the masticatory muscles occurs during dental procedures, it can involve local anesthesia administration. For example, accidental penetration of the medial pterygoid muscle during an inferior alveolar nerve block or a hematoma forming in the pterygomandibular space following injury to the inferior alveolar artery or vein can lead to trismus.1
Reference
1. Santiago-Rosado, L.M., Lewison, C.S. Trismus. (2022, October 27). StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK493203/
